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Chapter 9. Editors, Text Tools, Graphics, and Printing

In the next few chapters, we'll introduce a number of popular applications for Linux. We'll start here with text editing, which underlies nearly every activity on the system. (You need an editor to create a file of more than trivial size, whether it is a program to be compiled, a configuration file for your system, or a mail message to send to a friend.) On a related topic, we'll show you some text formatters that can make attractive documents and utilities that manage printing.

9.1. Editing Files Using vi

In this section, we're going to cover the use of the vi (pronounced "vee-eye") text editor. vi was the first real screen-based editor for Unix systems. It is also simple, small, and sleek. If you're a system administrator, learning vi can be invaluable; in many cases, larger editors, such as Emacs, won't be available in emergency situations (for instance, when booting Linux from a maintenance disk).

vi is based on the same principles as many other Unix applications: that each program should provide a small, specific function and be able to interact with other programs. For example, vi doesn't include its own spellchecker, or paragraph filler, but those features are provided by other programs that are easy to fire off from within vi. Therefore, vi itself is a bit limited, but is able to interact with other applications to provide virtually any functionality you might want.

At first, vi may appear to be somewhat complex and unwieldy. However, its single-letter commands are fast and powerful once you've learned them. In the next section, we're going to describe Emacs, a more flexible editor (really an integrated work environment) with an easier learning curve. Do keep in mind that knowing vi may be essential to you if you are in a situation where Emacs is not available, so we encourage you to learn the basics, as odd as they may seem. It should also be added that there are now a number of vi clones available that are much more comfortable to use than the original vi. These include vim (vi improved) and nvi (new vi). Chances are that your distribution has things set up so that when starting vi, you actually start one of those. We'll stick to the basics here, though so that you can use the information presented here no matter which version of vi you use. You can find coverage of the newer versions in the book Learning the vi Editor by Linda Lamb and Arnold Robbins.

9.1.2. Inserting Text and Moving Around

While using vi, at any one time you are in one of three modes of operation. These modes are known as command mode, edit mode, and ex mode.

After starting vi, you are in command mode. This mode allows you to use a number of (usually single-letter) commands to modify text, as we'll see soon. Text is actually inserted and modified within edit mode. To begin inserting text, press i (which will place you into edit mode) and begin typing:

Now is the time for all good men to come to the aid of the party. 


~
~
~
~
~

While inserting text, you may type as many lines as you wish (pressing the Enter key after each, of course), and you may correct mistakes using the Backspace key. To end edit mode and return to command mode, press the Esc key).

While in command mode, you can use the arrow keys to move around the file. Alternatively, you may use h, j, k, and l, which move the cursor left, down, up, and right, respectively.

There are several ways to insert text other than using the i command. The a command (for "append") inserts text after the current cursor position. For example, use the left arrow key to move the cursor between the words good and men:

Now is the time for all good men to come to the aid of the party. 


~
~
~
~
~

Press a, type wo, and then press Esc to return to command mode:

Now is the time for all good women to come to the aid of the party. 


~
~
~
~
~

To open a line below the current one and begin inserting text, use the o command. Press o and type another line or two:

Now is the time for all good women to come to the aid of the party. 
Afterwards, we'll go out for pizza and beer.


~
~
~
~

Remember that at any time you're either in command mode (where commands such as i, a, or o are valid) or in edit mode (where you're inserting text, followed by Esc to return to command mode). If you're not sure which mode you're in, press Esc. This takes you out of edit mode, if you are in it, and does nothing except beep if you're already in command mode.

9.1.3. Deleting Text and Undoing Changes

From command mode, the x command deletes the character under the cursor. If you press x five times, you end up with the following:

Now is the time for all good women to come to the aid of the party. 
Afterwards, we'll go out for pizza and  


~ 
~ 
~ 
~

Now press a and insert some text, followed by Esc:

Now is the time for all good women to come to the aid of the party. 
Afterwards, we'll go out for pizza and Diet Coke. 


~ 
~ 
~ 
~

You can delete entire lines using the command dd (that is, press d twice in a row). If your cursor is on the second line, dd will produce the following:

Now is the time for all good women to come to the aid of the party. 
~ 
~ 
~ 
~ 
~

Text that is deleted may be reinserted using the p command (for "put"). Pressing p now will return the deleted line to the buffer after the current line. Using P (uppercase) instead will insert the text before the current line. By default, p and P insert text from the "undo buffer"; you can also yank and replace text from other buffers, as we'll see later.

The u command undoes the latest change (in this case, pressing u after dd is equivalent to p). If you inserted a large amount of text using the i command, pressing u immediately after returning to command mode would undo it.

To delete the word beneath the cursor, use the dw command. Place the cursor on the word Diet and type dw:

Now is the time for all good women to come to the aid of the party. 
Afterwards, we'll go out for pizza and Coke. 


~ 
~ 
~ 
~

9.1.5. Moving Commands

You already know how to use the arrow keys to move around the document. In addition, the w command moves the cursor to the beginning of the next word; b moves it to the beginning of the current word. The 0 (that's a zero) command moves the cursor to the beginning of the current line, and the $ command moves it to the end of the line.

When editing large files, you'll want to move forward or backward through the file a screen at a time. Pressing Ctrl-F moves the cursor one screen. forward, and Ctrl-B moves it a screen backward.

In order to move the cursor to the end of the file, type G. You can also move to an arbitrary line: the command 10G would move the cursor to line 10 in the file. To move to the beginning of the file, use 1G.

Typing / followed by a pattern and the Enter key causes you to jump to the first occurrence of that pattern in the text following the cursor. For example, placing the cursor on the first line of text in our example, and typing /burg moves the cursor to the beginning of the word "burgers." Using ? instead of / searches backward through the file.

The pattern following a / or ? command is actually a regular expression. Regular expressions are a powerful way to specify patterns for search and replace operations and are used by many Unix utilites. (The manual page for ed describes regular expressions in some detail.) Using regular expressions, you could, for example, search for the next uppercase letter, using the command:

/[A-Z]
Therefore, if the pattern you're searching for is not a static string, regular expressions can be used to specify just what you want.

You can couple moving commands with other commands, such as deletion. For example, the command d$ will delete everything from the cursor to the end of the line; dG will delete everything from the cursor to the end of the file.

9.1.7. Editing Another File

To edit another file, use the :e command. For example, to stop editing test, and edit the file foo instead, use the command shown at the bottom of the following box:

NOW IS THE TIME FOR ALL GOOD WOMEN TO COME TO THE AID OF THE PARTY. 
Afterwards, we'll go out for burgers and fries. 
~ 
~ 
~ 
~ 
:e foo 


If you use :e without writing the file first, you'll get the error message:

No write since last change (:edit! overrides)
At this point, you can use :w to save the original file, and then use :e, or you can use the command :e! foo, which tells vi to edit the new file without saving changes to the original.

9.1.10. Global Searching and Replacing

There are many more features of vi than are documented here; most of these features are simply implemented through combinations of the simple features we've seen. Here are one or two other tidbits most vi users find useful.

The command:

:[x,y]s/pattern/replacement/flags
searches for pattern between lines x and y in the buffer, and replaces instances of pattern with the replacement text. pattern is a regular expression; replacement is literal text but can contain several special characters to refer to elements in the original pattern. The following command replaces the first occurrence of weeble with wobble on lines 1 through 10 inclusive:
:1,10s/weeble/wobble

Instead of giving line-number specification, you can use the % symbol to refer to the entire file. Other special symbols can be used in place of x and y. $ refers to the last line of the file. Leave x or y blank to refer to the current line.

Among the flags you can use are g to replace all instances of pattern on each line, and c to ask for confirmation for each replacement. In most instances, you will want to use the g flag, unless you want to replace only the first occurrence of pattern on each line.

You can also use marks to refer to lines. Marks are just single-letter names that are given to cursor locations within the document. Moving the cursor to a location in the file and typing ma will set the mark a at that point. (Marks may be named any of the letters a-z or A-Z.) You can move the cursor directly to the mark a with the command `a (with a backquote). Using a regular single quote (as in 'a) will move the cursor to the beginning of the line that the mark a is on.

Marks allow you to "remember" cursor locations that denote a region of text. For example, if you want to search and replace a block of text, you can move the cursor to the beginning of the text, set a mark, move the cursor to the end of the text, and use the command:

:`a,.s/weeble/wobble
where `a refers to the line containing mark a, and . refers to the current line.

9.1.11. Moving Text, and Using Registers

One way to copy and move text is to delete it (using the d or dd commands) and then replace it with the P command, as described earlier. For example, if you want to delete the 10 lines, starting with the line that contains the cursor, and paste them somewhere else, just use the command 10dd (to delete 10 lines), move the cursor to the new location for the text, and type p. You can copy text in this way as well: typing 10dd followed by P (at the same cursor location) deletes the text and immediately replaces it. You can then paste the text elsewhere by moving the cursor and using p multiple times.

Similar to dd is the yy command, which "yanks" text without deleting it. You use p to paste the yanked text as with dd. The deletion and yank commands can be used on more general regions than lines. Recall that the d command deletes text through a move command; for example, d$ deletes text from the cursor to the end of the line. Similarly, y$ yanks text from the cursor to the end of the line.

Let's say you want to yank (or delete) a region of text. This can be done with marks as well. Move the cursor to the beginning of the text to be yanked and set a mark, as in ma. Move the cursor to the end of the text to be yanked and use the command y`a. This yanks text from the cursor position to the mark a. (Remember that the command `a moves the cursor to the mark a.) Using d instead of y deletes the text from the cursor to the mark.

The most convenient way to cut, copy, and paste portions of text within vi is to use registers. A register is just a named temporary storage space for text you wish to copy between locations, cut and paste within the document, and so forth.

Registers are given single letter names; any of the characters a-z or A-Z are valid. The " command (a quotation mark) specifies a register; it is followed by the name of the register, as in "a for register a. The lower-case letters and their upper-case counterparts refer to the same registers: using the lower-case letter overwrites the previous contents of the register and using the upper-case letter appends to it.

For instance, if we move the cursor to the first line in our example:

NOW IS THE TIME FOR ALL GOOD WOMEN TO COME TO THE AID OF THE PARTY. 
Afterwards, we'll go out for burgers and fries. 
~ 
~ 
~ 
~

and use the command "ayy, the current line is yanked into the register a. We can then move the cursor to the second line, and use the command "ap to paste the text from register a after the current line:

NOW IS THE TIME FOR ALL GOOD WOMEN TO COME TO THE AID OF THE PARTY. 
Afterwards, we'll go out for burgers and fries. 
NOW IS THE TIME FOR ALL GOOD WOMEN TO COME TO THE AID OF THE PARTY. 
~ 
~ 
~

Similarly, the command "ay`a yanks text from the cursor to mark a into register a. Note that there is no correspondence between mark and register names!

Using registers allows you copy text between files. Just copy the text to a register, use the :e command to edit a new file and paste the text from the register.

9.1.12. Extending vi

vi is extensible in many ways. Most of the commands we've introduced can be generalized to arbitrary regions of text. As we've already seen, commands such as d and y operate on the text from the cursor to a move operation, such as $ or G. (dG deletes text from the cursor to the end of the file.) Many other commands operate on text through a move command in the same way. Using marks you can operate on any region of text.

As we mentioned before, vi is just a text editor; it doesn't have facilities for spellchecking text, compiling programs, and other such features. However, vi executes other programs, which you can use to extend the editor. The command:

:x,y!command
executes the named command with the text on lines x through y as standard input, and replaces the lines with the standard output of the command. As with the s (search and replace) command, other specifications such as % and $ can be used for the line numbers.

For example, let's say you want to prepend a quote character (>) to all of the lines in a region of text. One way to do this is to write a short shell or Perl script (see Chapter 13, "Programming Languages") that reads lines of input and outputs those same lines with the quote character prepended. (Or use a sed command; there are many alternatives.) You can then send lines of text through this filter, which replaces them with the quoted text within vi. If the script is called quote just use a command such as

:`a,.!quote
which quotes the region of text between the cursor location and the mark a.

Be familiar with the various ex commands that are available. The :set command allows you to set various options; for example, :set ai turns on auto indentation of text. (:set noai turns it off.)

You can specify ex commands (such as :set) to execute when starting up vi in the file .exrc in your home directory. (The name of this file can be changed with the EXINIT environment variable.) For example, your .exrc file might contain:

set ai
to turn on autoindentation. You don't need the : before ex commands in this file.

There are a number of good tutorials and references for vi available--both online as well as in print. Learning the vi Editor is a good place to look for more information. If you have Internet access, the comp.editors archives for vi contain a number of reference and tutorial documents, as well as interesting vi hacks. ftp://alf.uib.no: /pub/vi is the archive home site; it is mirrored at cs.uwp.edu and elsewhere.



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